<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
	<title></title>
</head>
<body>
    <div>
	  <label><input type="radio" onclick="switchItem('外单位')" name="radio" />外单位</label>
	  <label><input type="radio" onclick="switchItem('本单位')" name="radio" />本单位</label>
	</div>
 
	<div>
	  <select id="s1" style="display:none">
		   <option>外单位A1</option>
		   <option>外单位A2</option>
		   <option>外单位A3</option>
	  </select>
	</div>
	<div>
	  <select id="s2" style="display:none">
		   <option>本单位A1</option>
		   <option>本单位A2</option>
		   <option>本单位A3</option>
	  </select>
	  <select id="s3" style="display:none">
		   <option>本单位B1</option>
		   <option>本单位B2</option>
		   <option>本单位B3</option>
	  </select>
	</div>
</body>
<script type="text/javascript">
  function switchItem(tag){
   var s1 = document.getElementById('s1');
   var s2 = document.getElementById('s2');
   var s3 = document.getElementById('s3');
   if(tag=='外单位'){
    s1.style.display = 'inline-block';
    s2.style.display = 'none';
    s3.style.display = 'none';
   }
   else{
    s1.style.display = 'none';
    s2.style.display = 'inline-block';
    s3.style.display = 'inline-block';
   }
  }
 </script>
</html>